Growth Rate of Chlorella in Flashing Light.

Abstract

Growth rate of the alga, Chlorella pyrenoidosa, has been measured at 25°C, as a function of intensitv and intermittency of illumination. The saturation curve obtained in continuous light shows a compensation point of less than 1000 erg/cm2-sec or 24 fc and an approximate saturation point at 25 x 103 erg/Cm2- sec or 600 fc. Intermittent light was obtained by sector chopping of a beam of 230 x 103 erg/cm2-sec to give light flashes of 1, 4, 17, and 67 milliseconds and various dark periods. With one millisecond flashes the alga almost completely integrates intensity times time so that growth response to integrated light intensity is the same as that observed in continuous illumination. With longer flashes the degree of integration decreases but remains significant even at 67 milliseconds. The intermittent light data have been treated also in terms of flash yield and compared with those of investigations on photosynthesis. Comparison of the critical data of the several investigfations reveals a range of variation which is not explainable in terms of the classical arguments used to explain the intermittency phenomena observed with very short flashes. The results allow prediction that partial, but probably not complete, advantage of the intermittency phenomenon may be taken to increase the efficiency of light utilization of an algal culture by turbulence of suspension.